In running, the pelvis acceleration will be roughly a constant -1 g during the flight phase and a peak of about +1 g during the stance phases. The stance phase pattern will be similar to the vertical ground reaciton force. Because the accelerometer also senses gravity, the flight phase may show up as zero g and the stance phase as +2 g. It depends on how you "zero" the accelerometer.

Then you have the impact peaks superimposed on this sinusoidal signal. Your accelerometer is attached well enough that the impact peaks show up, which is good, so you can measure their amplitude.

That's what I meant.